As shown in FIG. 1, a wireless communication system with multicast transmission comprises generally one data transmitter and multiple data receivers that receive data from the multicast transmitter. The data is transmitted simultaneously to all receivers using the same radio resource (e.g. logical data channel, physical data channel) but the quality of the received signal is generally not identical for all receivers. Some sort of feedback can be provided from the multicast receivers to the multicast transmitter.
There are many analogies between wireless and TCP/IP multicast scenarios. For more information on multicasting, it can be referred to Murhammer, Atakan, Bretz, Pugh, Suzuki, Wood, “TCP/IP Tutorial and Technical Overview”, 6th edition, Prentice-Hall, Upper Saddle River, N.J.: Chapter 2.1.4.2.
Feedback in multicast wireless systems can be used in various ways, for example:                The feedback can signify the positive or negative acknowledgement to the data reception;        The receivers convey information about the quality of the radio link;        The receivers request certain actions or procedures from the transmitter for data transmission, e.g. increase transmit power, improve coding gain, lower data rate etc.        
Such feedback is transmitted either from each multicast receiver or from only one designated multicast receiver, as known for example from US 2001/0046875 and EP 1 143 635.
The transmission of feedback is of course dependant on the design of the communication system. As an example, feedback can be transmitted periodically after a certain time interval has elapsed. Alternatively, the feedback is transmitted as a reaction to a certain event, such as a number of consecutive errors. Those skilled in the art will easily identify a huge variety of possibilities exceeding the aforementioned modes.
Sometimes the multicast data does not have to be received error-free in all receivers to satisfy the customer. For example, in the transmission of video data, the customer might still be satisfied if a sufficient number of video frames is received in good condition. There exist also transmission systems where part of the data is of higher importance than other data. An example is the MPEG standard, where generally the so-called I-pictures are of higher importance than P- or B-pictures (for further details, see Mitchell, Pennebaker, Fogg, LeGall, “MPEG Video Compression Standards”, Chapman & Hall, New York N.Y., 1997: Chapter 2.3.1).
Moreover, a high amount of feedback, which is signalled from the receiver to the transmitter generally decreases the data throughput efficiency. Hence, it is desired to decrease the feedback to the absolute minimum sufficient to satisfy a certain quality of service (QoS) for a customer.
In addition, by focusing on the delivery of important data, the link budget (e.g. power allocation, error resilience) can be exploited more efficiently. This will have a positive effect on the whole network (e.g. cell in a wireless network), as e.g. interference can be reduced.